In the field of integrated circuit packaging, the cost and size of the overall package are major concerns. Any reduction in the cost of producing the package or reduction in the size or thickness of the package can provide a significant commercial advantage. To this end, the packaging of integrated circuits is continuously being improved to provide higher performance and more cost effective integrated circuit packages.
There are currently several types of Ball Grid Array (BGA) packages currently available. These types include the Plastic Ball Grid Array (PBGA), the Ceramic Ball Grid Array (CBGA), and the Tape Ball Grid Array (TBGA). The PBGA and the TBGA are the thinnest ball grid array packages currently available. Referring to FIG. 1, a side plan view of a typical BGA integrated circuit package 10 will be described. Package 10 includes a dielectric substrate 12 an integrated circuit die 14, an array of bonding wires 16, an encapsulating material 18, and an array of contacts or solder balls 20.
As shown in FIG. 1, substrate 12 has a top surface 22, a bottom surface 24, a plurality of electrically conductive terminal pads 26 on the top surface 22 of substrate 12, a plurality of contact terminal pads 28 on the bottom surface 24 of substrate 12, and a plurality of electrically conductive traces (not shown). Each of the electrically conductive traces interconnects a respective one of terminal pads 26 on the top of substrate 12 to an associated contact terminal pad 28 on the bottom of substrate 12. Substrate 12 is made from a rigid material capable of supporting the other components of the package during the assembly of the package. Substrate 12 can be made of a material such as Polyvinyl Chloride (PVC). Integrated circuit die 14 has a top surface 30, a bottom surface 32, and includes a plurality of input/output terminals 34 on its top surface 30. Each of the bonding wires 16 electrically connect a respective one of terminal pads 34 to an associated terminal pad 26 on the top surface of substrate 12. Bonding wires 16 are wirebonded between terminal pads 34 of integrated circuit die 14 and terminal pads 26 through techniques that use ball and wedge bonds. Encapsulating material 18 encapsulates integrated circuit die 14, at least the top surface of substrate 12, and bonding wires 16. Contacts or solder balls 20 are attached to associated contact terminal pads 28 thereby allowing external electrical elements to be electrically connected to integrated circuit die 14. This arrangement represents the typical prior art PBGA integrated circuit package.
As is commonly understood, the surface area of die 30 is not large enough to allow multiple, individual conductive balls to be formed on its input/output contact pads. Therefore, dielectric substrate 12 is used to connect the closely spaced input/output contact pads of die 30 to contacts or solder balls 20 that are sufficiently spaced apart on the larger bottom surface 24 of dielectric substrate 12. In this way, package 10 can be conveniently attached to an external electrical system such as a printed circuit board through the contact 20.
Unfortunately, substrate 12 presents various cost and performance inefficiencies. First of all, the cost of PVC is a major cost driver for manufacturing BGA packages. Second, the distance that each of the electrically conductive traces travel within substrate 12 tends to be large enough to cause a noticeable decrease in system performance, especially at high frequencies. The length of each electrically conductive trace is large because each trace runs from a terminal pad 34 on the top surface 22, through the body of substrate 12, and then terminates at one of terminal pads 28 on bottom surface 24 of substrate 12. Third, substrate 12 typically can contain only a relatively low density of internal electrically conductive traces, which limits the maximum number of input/output contact points for integrated circuit package 10. Furthermore, the manufacturing yield of the substrates is low due to difficulties with forming the conductive traces within the body of the substrates. Finally, the manufacturing costs of substrates are high due to the need manufacture specific substrates to match the various sizes of integrated circuit dice.
Bonding wires 16 are another source of cost and performance inefficiencies for BGA packages because of the inaccuracy of wire bonding techniques, the space occupied by the bonding wires, and the likelihood of bonding wires 16 to become disconnected. The wire bonding processes also have occasional problems such as when wires do not properly attach to a contact point. Bonding wires can also get “washed” during an injection molding process where wires are pushed down, are pushed into contact with each other, or pushed into other problematic positions.